Thermogravimetric investigation of the lead volatilization from waste cathode-ray tube glass

Abstract

The treatment of lead-containing cathode-ray tube (CRT) glass is an important environmental issue. One approach is the removal of lead by chloride volatilization. In the present work, the reaction of CRT glass with PVC as the chlorinating agent and Ca(OH)2 as the chlorine absorber was investigated by thermogravimetric analysis (TGA) in air. Seven reaction steps occurring at different temperatures were identified as dehydrochlorination of PVC/HCl absorption, CO2 absorption, Ca(OH)2 dehydration, PVC derived char oxidation, PbCl2 formation and volatilization, CaCO3 decarbonation, and CaCl2 volatilization. Kinetic analysis of the PbCl2 volatilization showed that the reaction of CRT glass during TGA resembles that of amorphous PbSiO4, while the reaction in the tube reactor was similar to that of crystalline PbSiO4. Crystallization accelerates PbCl2 volatilization, and it might be advantageous for lead removal to crystallize the glass deliberately before or during treatment in order to reduce processing time and increase efficiency.